Impulse operated, day-night, rear view mirror

ABSTRACT

A day-night mirror for a vehicle, photo-electrically controlled in response to light directed from rearwardly of the vehicle and to ambient light, impinging respectively on photocells which via capacitive coupling control the motion of a reversible motor, in the form of a bifilar solenoid, so that only a change in status of the photocells is communicated to the motor in the form of a pulse leaving the motor to be freely actuated manually absent such a pulse, and also reducing the current drain in the system.

United States Patent 1191 Brean et al.

[ IMPULSE OPERATED, DAY-NIGHT, REAR VIEW MIRROR [75] Inventors: John W.Brean; Yervand Mathevosian, both of Cincinnati, Ohio [73] Assignee: D.H. Baldwin Company, Cincinnati,

, Ohio [22] Filed: Apr. 16, 1973 [21] Appl. No.: 351,559

Related US. Application Data [62] Division of Ser. No. 180,547, Sept.15, 1971.

[52] US. Cl. 318/480 [51] Int. Cl 1102p 11/00, HOlj 39/12 [58] Field ofSearch 318/480 [56] References Cited UNITED STATES PATENTS 3,003,09610/1961 Du Bois 318/480 X [451 Oct. 1,1974

3,621,356 11/1971 Kwan ChiOn ..318/480 3,641,413 2/1972 Ohntrupctal...3l8/48O Primary ExaminerB. Dobeck Attorney, Agent, or Firml-lymanl-lurvitz 5 7 ABSTRACT A day-night mirror for a vehicle,photo-electrically controlled in response to light directed fromrearwardly of the vehicle and to ambient light, impinging respectivelyon photocells which via capacitive coupling control the motion of areversible motor, in the form of a bifilar solenoid, so that only achange in status of the photocells is communicated to the motor in theform of a pulse leaving the motor to be freely actuated manually absentsuch a pulse, and also reducing the current drain in the system.

2 Claims, 3 Drawing Figures IMPULSE OPERATED, DAY-NIGHT, REAR VIEWMIRROR BACKGROUND This application is related in subject matter to anapplication of John Brean, Ser. No., 157,941 filed June 29, 1971, nowUS. Pat. No. 3,722,984'and entitled Day-Night Mirror for Vehicles, andto an application of Jordan et al., Ser. No. 24,593, filed Apr. 1, 1970,and entitled Photoelectrically Controlled Rear View Mirror, bothapplications being assigned to the assignee of this application.

In the prior Brean application a photocell which senses ambient lightand another photocell which senses light arriving from rearwardly of avehicle cooperate to control a transistor circuit, which directly, i.e.,not via relays, controls a motor which modifies the attitude of a mirrorwith respect to a pane of glass. The latter is so oriented that itreflects light to the eyes of a driver of the vehicle at all times. Apane of glass, when uncoated, reflects only a small fraction of thelight impinging thereon, so that if the mirror is so oriented that itdoes not reflect light toward the eyes of the driver, the driver canview rearwardly of the vehicle without glare. If the mirror is orientedin a plane parallel to the plane of the pane of glass, it becomes theprimary refleeting surface viewed by the driver, the pane of glass beingrelatively of minor effect, and the optical system composed of the paneof glass and the mirror are then suitable for night driving.

In the Jordan et al application, supra, ambient sensing and rearwardlooking photoelectric cells are dc coupled to a solenoid which drivesthe mirror to its alternate orientations via transistor circuitry,including power transistors, one of which is rendered conductive todrive the solenoid in one sense, and the other of which is renderedconductive to drive the solenoid in the opposite sense. One or the otherpower transistor is then always energized, the overall system beingbistable. The mirror can then not be readily normally moved from theorientation called for by the status of the photocells, and if so movedtends to move back when released. The system involves a continuous andsubstantial current drain through the solenoid coil.

The system of the present invention is a variant of the system of Jordanet al, in which the photocells are only ac coupled to the solenoid viatransistors, so that the latter only impulsively reverse the directionof drive of the solenoid armature, which is then releasably latched inits final position, but which can have its position modified manually,without having to overcome electrical forces due to current in thesolenoid. The solenoid and its energizing transistors normally carry nocurrent, in the present system.

SUMMARY A day-night mirror which is photo-electrically controlled bymeans of an ac coupled transistor circuit, utilized to drive a solenoidmotor which positions the mirror, the solenoid being supplied withcurrent by transistors which are normally cut off, and which carrycurrent only during transitions of mirror position.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a systemaccording to the present invention;

FIG. 2 is a view in side elevation of a solenoid drive for a day-nightmirror; and

FIG. 3 is a circuit diagram of a modification of the circuit diagram ofFIG. 1.

DETAILED DESCRIPTION Q1 and Q2 are NPN transistors connected in abistable configuration. The emitters of Q1 and Q2 are connected toground through a common resistance R1, but they have separate collectorloads R2 and R3, respectively. If O1 is cut off, its collector is atsupply potential, +l2.V, and the base of Q2 being connected to thecollector of Q1, O2 is conductive. If O1 is conductive the base of O2 isgrounded, and its emitter at the voltage across RI, and it is thereforenonconductive.

The conductivity of O1 is determined by its base voltage, which in turnis established at junction 10, between two photo-resistors 11 and 12.Photoresistor 11 at one terminal is connected to voltage supply bus 13via a resistance R4 of about K, and at its other terminal to junction10. Junction 10 is connected to ground via photocell 12, which isparallel by a large transient by-pass capacitor C, and 150.I(resistance, and by a larger variable resistance R5 in series with asmaller fixed resistance R6.

In daylight both photo-resistors 11 and 12 are fully illuminated and ofvery small resistance. The base of O1 is grounded, R4 absorbing supplyvoltage, O1 is cutoff and O2 is conductive. Q3 and 04 are unaffected bythe state of 02, because capacitor C2 isolates the base of 03 from thecollector of Q2. Q3 has its base connected to ground through resistanceR7 and is therefore cut off. The base of O4 is connected to groundthrough resistance R8 and is also cut off, R8 acting both to ground thebase of Q4 and as an emitter load for Q3. The collector of O3 isconnected to supply bus 13 via a very small resistance R9, but O4 isavailable to supply current to one winding N of a bifilar solenoid coilS. That winding is normally de-energized. Q6 and Q7 operate precisely asdo 03 and Q4, but 07 is available to supply current to a second bifilarwinding D of solenoid coil S, and accordingly winding D is normallyde-energized.

Photo-resistor 11 looks rearwardly of the vehicle on which it ismounted, and photo-resistor 12 looks sideways, particularly to the left,so that 11 is responsive to a light approaching from the rear of thevehicle as well as to ambient light, but 12 only to ambient light.

Q5 conducts when O2 is non-conductive, and vice versa, since the base ofO5 is connected via a small resistance R10 to the collector of Q2. Ittherefore follows that if O2 is rendered conductive, Q5 will be renderednon-conductive, and that during the transition of Q3, Q4 will be drivenby a negative pulse and Q6, 07 by a positive pulse. If O2 is renderednon-conductive, Q5 will be rendered conductive, and Q3 and Q4 will bedriven by a positive pulse but Q6, Q7 by a negative pulse. Negativepulses have no effect on transistors which are cut off, but positivepulses cause current flow, and accordingly one of the windings N and Dwill be energized. These drive armature A of solenoid S in oppositedirections, and tilt mirror 7 respectively into night and day positions.

So long as daylight persists the mirror is in its day position. We mayassume that it was so positioned manually, via manual lever ML.

At night, both photo-resistors l1 and 12 are dark, assuming no followingheadlamps, but photo-resistor 12 is by-passed by resistances R5, R6, ofmuch smaller resistance than inheres in the photo-resistors. Point 10 isthen essentially at ground voltage, Q1 is cutoff, and O2 is conductive.

If a following vehicle illuminates photo-resistor 11, photo-resistor 12remaining dark at night, the voltage of point 10 rises, Q1 becomesconductive, Q2 nonconductive, the voltage at the collector of Q2 rises,a pulse is transferred via C2 to the base of Q3, which becomesconductive, driving Q4 into conductivity and energizing coil N to placethe mirror in night orientation or condition. As soon as the rearwardvehicle passes, the voltage of point 10 decreased toward ground. Q2becomes conductive, which has no effect on N. The drop in voltage at thecollector of Q2 is communicated to Q5, which cuts off, passing anenergizing pulse to Q6, Q7, and transiently energized D.

The mirror M is accordingly normally in fully reflecting orientation,day or night, until and unless a rearward vehicle approaches and itsheadlights illuminate photo-resistor 11. At that time the mirror M ismoved by coil N via cam C so that it no longer reflects light to theeyes of the driver and this condition obtains until photo-cell 11 is nolonger illuminated by the following headlamp, when a transient positivepulse occurs to coil D, pulling the mirror back to its normal condition.

Photoresistors 11, 12 are not on-off devices, but vary theirresistivities according to the intensities of impinging light. The valueof resistance R can be set such that Q1 will not change state until thelight impinging on 11 attains a predetermined value under predeterminedambient conditions. For fully dark ambient conditions photoresistor 12represents megohms, so that the division of voltage betweenphoto-resistors 11 and R6, R5 is not determined by the value of R5. Butif a rearward headlight is far off, but provides some light, theresistance of 11 is of the order of the resistance of R5, and thepotential of junction therefore rises from zero in total darkness, to apositive value, as rearward illumination increases, until for some valueof illumination pre-established by the setting of R5, Q1 changes state,and with it Q2.

It follows that the coils of solenoid S are energized only transiently,and are not normally energized at all. This leaves the mirror free to bepositioned manually, and the manual actuator need only overcome magneticdetent force at permanent magnets PM, but not current flow to thesolenoid coils D and N. No current normally flows to these coils, andimpulsive current is caused to flow to the proper one of coils D and Nas external conditions of ambient and rearward illumination change,while driving. An important advantage is that the present system may bedry battery driven, if desired, without undue battery drain, and doesnot present a continuous drain on the power source employed, whether asmall dry or a large wet battery constitutes that source. The actualphysical construction of the mirror and mirror motor and latch is thatof Jordan et al., supra, and details are not repeated here.

The capacitor C is in a sufficiently long time constant circuit thatchanges in voltage thereacross require substantial time, so that shorttransient illuminations of either photo-resistor 11 or photo-resistor 12or both can not affect the bias on Q1.

In FIG. 3, the photo-cell circuit, involving photoresistors 11, 12 andthe associated resistances R4, R5, R6, and capacitor C, together withbistable network involving Q1, Q2 and OS, are identical with thecorresponding elements of FIG. 1, and serve the same purposes, andthereafter the description of the circuitry and of its operation is notrepeated.

Q10, Q12 and Q13 are unaffected by the state of 02, because capacitor C2isolates the base of Q10 from collector of Q2. Q10 has its baseconnected to ground through resistance R7 and is therefore cut off. Q10being non-conductive, the base and emitter of transistor Q12 are then atthe same potential, as are the base and emitter of Q13. Thesetransistors are therefore non-conductive and winding 50 is notenergized.

Q11, Q14 and Q15 are unaffected by the state of Q5 as are Q10, Q12 andQ13 by the state of Q2. Q5 conducts when O2 is non-conductive and viceversa, since the base of Q5 is connected via resistance R10 to thecollector of Q2. It therefore follows that if Q2 is rendered conductive,Q5 will be rendered non-conductive, and that during the transition Q10will be driven by a negative pulse and Q11 by a positive pulse. If 02 isrendered non-conductive, Q5 will be rendered conductive, and Q10 will bedriven by a positive pulse, but Q11 by a negative pulse. Negative pulseshave no effect on transistors which are cut off, but positive pulsescause current flow. When a positive pulse is applied to Q10,

it turns on. The voltage drop across R11 then renders Q12 conductive,the drop across R13 renders Q13 conductive, and winding 50 is pulsed inthe direction from A to B.

Winding 50 schematically represents a dc. motor and is illustrated twicein FIG. 3 solely to indicate its alternative directions of energizationaccording as to whether Q12, Q13 or Q14, Q15 are conductive.

If a positive pulse is applied to Q11, it is turned on. The voltage dropacross R14 then renders Q14 conductive, the drop across R16 renders Q15conductive, and winding 50 is pulsed in the direction of B to A.

If for coils 50 were substituted coils N and D, the circuit of FIG. 3could be used to drive the bifilar windings N and D of solenoid S.

What is claimed is:

l. A photo-resistor controlled motor circuit, comprising a backwardlooking photo-resistor, a side looking photo-resistor, means connectingsaid photoresistors in series across a voltage supply, therebyestablishing a junction between said photo-resistors, a bistable solidstate flip-flop circuit having one or another state according as saidjunction is sustained at a reference value in response to intensity ofillumination of said photo-resistors or departs substantially from saidreference value in response to differential illumination of saidphoto-resistors, separate normally nonconductive solid state switchesconnected respectively to supply current to said motor in oppositesenses from said voltage supply and capacitive means coupling saidswitches to said motor in response only to transfer of said bistablecircuit in its alternative states and only during such transfers.

2. The combination according to claim 1, wherein said motor is asolenoid including armature means and coil means for actuating saidarmature means, said circuits for transferring only transient controlpulses of opposite polarities to said solid state switches,respectively, only during changes of state of said bistable solid statecircuit.

1. A photo-resistor controlled motor circuit, comprising a backwardlooking photo-resistor, a side looking photo-resistor, means connectingsaid photo-resistors in series across a voltage supply, therebyestablishing a junction between said photoresistors, a bistable solidstate flip-flop circuit having one or another state according as saidjunction is sustained at a reference value in response to intensity ofillumination of said photo-resistors or departs substantially from saidreference value in response to differential illumination of saidphotoresistors, separate normally non-conductive solid state switchesconnected respectively to supply current to said motor in oppositesenses from said voltage supply and capacitive means coupling saidswitches to said motor in response only to transfer of said bistablecircuit in its alternative states and only during such transfers.
 2. Thecombination according to claim 1, wherein said motor is a solenoidincluding armature means and coil means for actuating said armaturemeans, said solid state switches comprising a first normallynon-conductive solid state switch connected in series with said coilmeans, a second normally non-conductive solid state switch connected inseries with said coil means, and said coupling means including accoupling circuits for transferring only transient control pulses ofopposite polarities to said solid state switches, respectively, onlyduring changes of state of said bistable solid state circuit.